This invention relates to a switch assembly for use in high-voltage switching installations and, more particularly, in switching installations which are encapsulated in metal casings and insulated by means of compressed gas.
As described in U.S. Pat. No. 4,445,014, a disconnect switch for metal-encapsulated high-voltage switching installations, particularly installations insulated by means of compressed gas such as SF.sub.6, has a switching gap disposed between a pair of field electrodes. A tubular fixed contact is disposed in one of the field electrodes, while a tubular movable contact or main switching pin is disposed in the other of the field electrodes. The movable contact contains a spring loaded auxiliary switching pin which is engageable with a respective mating contact located in the fixed contact of the disconnect switch. The movable contact of the disconnect switch is operatively linked to a relatively slow drive, the auxiliary switching pin being provided in order to short the switching gap during a disconnecting operation. The auxiliary switching pin remains engaged with its mating contact until the movable main switching pin has reached a position at a distance from the fixed contact at least equal to the voltage breakdown limit of the insulating gas.
In the disconnect switch assembly described in U.S. Pat. No. 4,445,014, the fixed contact contains a mechanical control including stops and a ratchet which prevents the disengagement of the auxiliary switching pin and its mating contact until the main movable contact has reached the voltage breakdown position. Upon the release of the auxiliary switching pin from its mating contact in response to a triggering action by the mechanical control in the fixed contact, the auxiliary switching pin is returned by its loaded spring into the tubular movable contact with a speed greater than the motion thereof. Any low-current arc generated during the disconnecting operation is quickly interrupted owing to the high speed with which the auxiliary switching pin is separated from the ratchet. The speed of withdrawal of the auxiliary switching pin prevents an electrical arc from having sufficient time to travel to the grounded metal encapsulation and thereby to initiate a short to ground. Because the auxiliary switching pin and its mating contact are located in the "off" position in the interiors of the field electrodes, the electric field in the switching gap is not effected by their presence. During a circuit closing operation, the auxiliary switching pin is entrained or shifted along with the movable main switching contact until the pin has reached its mating contact and interlocks therewith.
The use of the above-described mechanical control including stops and a ratchet for preventing the withdrawal of the auxiliary switching pin until a predetermined position has been reached by the tubular movable contact has the disadvantage that extremely high specific pressures are necessary for locking the ratchet to the auxiliary switching pin, these pressures being requlred because of the large spring forces used for accelerating the auxiliary switching pin. The existence of such high pressures in the disconnect device results in a wear of the part.
U.S. Pat. No. 4,451,716 describes an elastic spring drive for shifting the movable switching pin of a disconnect switch. The elastic spring drive includes a cocking lever rotatably supported by a drive shaft and a drive lever rigidly contacted to the drive shaft. The free end of the drive lever is pivotably connected to one end of an elastic compression spring, the other end of which spring is pivotably connected to the free end of the cocking lever. The cocking lever is connected to an actuating lever movable in the direction of its longitudinal axis.
An object of the present invention is to provide an improved switching assembly for use in metal-encapsulated high-voltage switching installations filled with compressed insulating gas.
A more particular object of the present invention is to provide such a switching assembly with a control triggering mechanism for the faster movement of the auxiliary switching pin in respect of the movable main switching pin, which trigger mechanism is as free from wear and tear as possible and, in addition, becomes effective in a specific position not only during the switching-on process, but also during the switching-off process.